GregBBRD

Baking soda has its own limitations. It is neither abrasive enough or durable enough to remove powder coating (or the epoxy coating) on the manifolds or valve covers.

I've stopped allowing my powder coating company to use silicon beads to remove the old material. I now insist that they sand blast. Yes, the base material gets "beat up" more, but the sand isn't as tough to get out from the corners.

Note that almost all powder coating companies will "soak" pieces in a giant vat of liguid that will soften the old paint/powder coating, so that less manual labor is required to remove the balance of the material. In the corners, this "soft" gummy left over material can seldom be removed by silicon beads....it simply traps the beads. Sand blasting blows this gummy stuff away.

Irregardless, I plan on a minimum of 4 hours to hand scrape and clean an S4 manifold, replace the bearings, and assemble it. Yes, that doubles the cost of very high quality powder coating....but this is the 4th or 5th engine I've done that has this exact problem.

That makes those 4 hours look pretty cheap....

JWise

Wow! Amazing what damage can be done in such a short period of time.

Sorry for your situation. Best wishes for getting it back on the road!

namasgt

This is nothing new, there has been several threads about this over the years. One time I helped tear down a 87 engine that would not hold compression due to the media working its way through out the engine. It looked a lot worse than the pictures in this thread. The bores looked as if someone had sanded on the walls with a 80 grit sand paper. It was really rough.

For me what worked after washing the intake with garden hose and in the bathtub and still finding sand media inside the intake was taking it to a car wash and pressure washing it for 5-10 minutes. Pressure washed each runner from both openings several times. Yes you will get soaked in water doing this.

Have done this on 3 different S4 intakes with success. Problem is you can easily chip the paint if you get the nozzle too close to the edges, but rather risk that than damage the engine.

I think that when you blast the media with high air pressure, some of the media (sand, glass,...) will get embedded into the casting surfaces and low pressure washing with a garden hose or sloshing the intake around inside a tub filled with water won't get all the media out.
I had a powder coated S4 intake some mechanic had supposedly cleaned well and had it build up and ready for install on to the engine. Luckily before that could happen I inspected the intake and could see shiny particles on the intake inside walls that would not wipe off with my finger, I could get a little bit of the shiny particles on my finger but most of it would not come off the surface. I end up disassembling the intake and taking it to a car wash and thoroughly pressure washing it for more than 5 minutes. Took it back to the garage dried it out and no more shiny particles on the casting walls and very clean to the touch.

Even if you think your intake is clean, inspect and look for any shiny particles on the casting surface (move the intake under a light). If you see any shinny particles, the intake has not been fully cleaned of all the media. So clean it good...

Imo000

I had an engine that had internals look.anlot like this. In my case the sand didn't come from the intake but from a catalytic converter that was part of an exhaust manifold (3.5L V6/Nissan), the converter matrix got loose, over time the decided pieces got sucked back into the engien because of the overlap of the cams and slowly wore away the engine. The rings looked exactly like the one in the picture. Engine had 0psi compression.

Reddog2

Thanks for posting - reminders are good.

I had my intakes coated a few years ago and no problems I am aware of. I cleaned them 3 or 4 times and just when I thought they were good, I cleaned them twice more.

I wouldn't have been so paranoid about cleanliness if I didn't read previous posts on its importance. I probably would have rinsed a few times and reinstalled.

atb

Thanks for sharing Vanster, these kinds of experiences cannot be posted enough when they happen.
Just shows that sometimes common diligence isn't enough to protect you from damage.
Is a hot tank an option for this kind of cleaning, or would that be too hard on the castings?

John Speake

Would a steam cleaner work better for removing the stubborn residuals ?

marine928

I have had my intake on my 87 blasted twice. Went the spray can route as well and hand painted the letters. The blaster did mask off everything but I still found black media. Used my 2500 psi pressure washer for at least 45 min from every angle.
I also changed out the "flappy" bearings to be on the safe side and found grit in the rollers as well. Highly recommended to change them out. The hardest part is removing them.

namasgt

Using a pressure washer is the way to go IMO.

Lizard928

I use a set of dental picks, brushes, and a 4000psi pressure washer with a rotary nozzle to blast everything out.

UKKid35

Sincere condolences.

How important is a freshly powder coated intake plenum?

Adk46

It's like wearing clean underwear. No, don't like that analogy. OK - it's like finally tossing out your ratty old underwear and getting new.

UKKid35

When was the last time your 'clean' underwear gave you syphilis.

Mark R.

Wow. Major condolences Van. That is quite a nightmare, and I admire your positive attitude.

I think the thread title is a little misleading. Powder coating, in and of itself, is probably not the cause.
Isn't it much more likely that it was due to the cleaning process, and whatever media remained inside?
Many folks who don't plan to powder coat, still use various blasting processes to clean and prep.
The point being:
Extreme diligence with the cleaning process, regardless of whether one plans to powder or liquid coat.
.

docmirror

Silica sand blast material is about 6-7 Mohs hardness. Diamond is 10. Each particle of silica has 16 facets(as I recall from semiconductor theory class). Outstanding as an abrasive.